Arrangement for reducing the stray reactance of cascade transformers



Feb. E8, 393%. E. PFIFFNER ARRANGEMENT FOR REDUCING THE STRAY REACTANCEOF CASCADE TRANSFORMERS 2 Sheets-Sheet 1 Filed NOV. 26, 1923 imveiizzzr5 hm.) $046k Fb. 1, 193@. PFIFFNER 1 747 528 ARRANGEMENT FOR REDUCINGTHE STRAY REACTANCE OF CASCADE TRANSFORMERS Filed Nov, 26, 1923 2Sheets-Sheet 2 Patented Feb. 18, 1930 UNITED STATES PATENT OFFICE EMILPFIFFNER, OF BUDAPEST, HUNGARY Application filed November 26, 1923,Serial No. 677,114, and in Germany November 28, 1922.

I This invention relates to improvements in arrangements for reducingthe leakage reactance of compound or cascade transformers.

and essentially consists in the provision of 6 compensating windingswhich convey and improve the electromagnetic interlinking between theprimary and secondary windings and the coupling windings respectively.

With the above object in view the-invention consists of certainnoveldetails of construction hereinafter fully described and claimed. I

Several modes of carrying out the present invention are illustrated byway of example on the accompanying sheets of drawings in which Fig. 1shows diagrammatically a compound or cascade transformer constructedaccord- I in to the present invention.

igs. 2 and 3 illustrate the constructive arrangement of compensating orequalizing windings. U

Figs. 4 and 5'illustrate in sectional el'evation and plan viewrespectively a compound or cascade transformer constructed according tothe present invention.

As shown in Fig. l the compound or cascade transformer comprises anumber of individual transformers connected in series.

By placing a number of such transformers one-on the other a transformerfor any voltage can be constructed. It is well known that such anarrangement has the advantage of simplification of manufacture by usingthe same coil elements for construction of apparatus for the most variedvoltages.

There is, however, the disadvantage that owing to differences in themagnetic resistance of the separate cores and the reaction of thesecondary windings in the coils of the diiferent cores differentvoltages are induced which affects the accuracy of the secondarywindings.

Owing to the magnetic leakage at the ends of the core inequalities occurin the magnetic flux of the iron core; this is very undesirable.

The object of this invention is to overcome these objections by means ofcompensating coils which are connected up in opposition to each otherand compensate any variation in the magnetic flux occurring in thecoils.

The other undesirable objection of inequalities in the magnetic flux ofthe iron core is overcome by the arrangement ofa further compensatingwinding. This winding comprises two coils connected in opposition toeach other, and arranged at the points of the magnetic circuits whichare to be mutually compensated.

Owing to the better electric insulation cascade transformers areemployed as hightension transformers particularly voltagetransformers,the said cascade transformers comprising a number of individual transformers connected in series, each of the latter being constructed andinsulated for a part of the voltage. Each of these individualtransformers is provided with a high-tension winding W W "W throughwhich the respective individual voltage is adapted to pass and which isin series with the other individual transformers. The beginning ofwinding of the first individual transformer is connected to therespective high-tension line and the end of winding is grounded. Inorder to attain the smallest insulation-stress, the iron members of theindividual transformers are constructively connected with the centre ofwinding of the respective part-members. T e grounded secondarywindings 8lies next to the hightension coil which is grounded.

The voltage drop between the individual transformers is increaseduniformly and therefore the secondary winding, whose volt also theelectromagnetic reaction of the secondary current has to be transferredto all individualtransformers. This cannot be ac complished by seriesconnection of all secondary windings, as otherwise all individualhigh-tension windings would require to be I the high-tension windings.

entirely insulated against earth connection and thus the entire compoundor cascade arrangement would be ofno use. Moreover the transfer of thesecondary reaction has to be accomplished by means of coupling windings,which. electromagnetically couple the upper end of one member with thelower end of the adjacent member. I

As shown in Fig. 1, W W W designate the transformer are connected to theiron cores f f f by means of connections U U and U Thecoupling windingsK and K and. K and K respectively are connected in opposition. 7 Theirefiects result therefrom, that f the secondary windings s of the flux inthe iron-core f is weakened, whereby a smaller tension is induced thanin the winding K so that a compensating or equalizing current will beproduced from the windings K to the winding K which hasthe tendency toincrease the flux in the iron core f and to reduce the flux in theiron-core f The weakening in the iron-core f will produce the sameeffect in the iron-core f over the coupling windings K and K and thusthe reaction of the secondary current is transferred to all members.

From the above it is clear, that the principle of construction of thesecompound or cascade transformers will lead to an axially displacedarrangement of primary and secondary windings, thus toa constructionwhich does not produce a good electromagnetic interlinking of thesewindings but a large leakage resistance. Therefore in practice thearrangement diagrammatically illustrated in Fig. 1 is of no use, asduring a secondary stress it will yield voltage drops which are far toolarge. These reactive drops produce an unsymmetricaldistribution of themagnetic flux in the magnetic iron in such a manner that-the flux isreduced in the direction of current along the axis of magnetic cores.

The arrangement hereinafter described reduces the leakage to a tolerabledegree by arranging on the iron-core a compensating or equalizingwinding a, a", which by means of a direct electrical connection with thesame is brought to the same electrical potential and which is disposedconcentrically with respect to the primary and secondary winding asdiagrammatically shown in Fig. 2.

The said compensating or equalizing winding consists of two coils whichare. connected in opposition and try to prevent the unsymmetrical fielddistribution produced by the able degree and the cascade arrangement maybe used for measuring purposes.

Fig. 3 illustrates diagrammatically the constructive arrangement of thecompensating or equalizing winding a, a". The iron-core 7 may be used asone of the two connections of the coils a, a.

In the arrangement illustrated in Fig.3 the best possibleelectromagnetic interlinking of the three windings is conclusive for thearrangement of the three windings with respect to one another.

Fig. 4 shows in longitudinal section 'a two stage cascade transformerprovided with the various windings above described. Fig. 5 is across-sectional view of the transformer shown in Fig. 4 and illustratesthe arrangement of the windings W and the iron-core W and W designatethe two series-connected high-tension windings to which are coaxiallycoupled the oppositely connected coupling windings k and k The couplingwinding k of the top unit is disposed at the bottom end of the winding'w while the coupling windings 7: of the bottom unit is located at thetop. end of the winding 'w The secondary winding .9 is disposed at thebottom end of the winding w These windings are insulated by aninsulating sleeve from the concentrically ar ranged compensating orequalizing windings a and a" of the bottom unit and a and a," of the topunit. The said compensating windings possess small induced tensions onlyand therefore need to be slightly insulated only with respect to theiron-cores f and f, respectively, so that the latter can be used aselectric return line connection.

The centres of the high-tension windings W and W are connected with theiron-cores f and f, by means of connections u and M in order todetermine the maximum tension of the insulatingsleeve between thehigh-tension windings and the iron-cores.

The operative parts of the two series-connected units are mounted ininsulating cases 6 and 6 which are cemented to the sleeves k. The bottomunit rests on an earthed base 9 in which are mounted secondaryterminals. A hood 0 provided with a terminal (1 for the high tensionline, is mounted on the top unit.

Fig. 5 shows the relative arrangement of the iron-core f and the windingW in the insulating case 6 I claim:

1. In a cascade transformer, a plurality of iron cores, a plurality ofseries connected high tension primary windings inductively wound withsaid cores, each being electrically connected to the middle point of itsrespective core, a secondary winding, coupling windings axiallydisplaced with respect to one another to efi'ect an equalization of themagnetic flux in said cores and compensating windings each consisting oftwo coils arranged on the-same iron core acting in opposite directionsand connected in oppositionwhereby the leakage reaatance of saidtransformer is reduced.

2. In a cascade transformer, a plurality of iron cores, a plurality ofseries connected high tension primary windings inductively wound withsaid cores each being electrically connected to the middle oint of itsrespective core,asecondary win ing, coupling windings axially displacedwith respect to one another to effect an equalization of the magneticflux in said cores and compensating windings comprising a pair ofoppositely Wound coils on the same iron, said iron core forming aconnecting link between said coils, whereby the leakage reactance ofsaid transformer is reduced.

In testimony whereof I hereunto afiix my signature.

EMIL PFIFFNER.

